Genetic Adaptation to Carbs
 

We all know the reasoning behind the success of the various low carb diets. Its because our ancestors ate this way and we are adapted well to it, modern agriculture and the advent of plentiful carbs being a relatively recent development (10,000 years give or take). We also hear a lot that genetic adaptation takes much longer than this, like 100s of thousands of years.

My question is this. If it takes so long to develop and adapt, why has there been such a large change in the looks of man over the last 100,000 years? And how is it that we have adapted such different features in the various cultures across the world? It would seem to me, that the differences in how we look from each other, and from our distant ancestors, says something about the rapidity of genetic change.

Whats more, we have cultural groups who have been at dairy farming in some form or fashion for thousands of years, and these folks are better adapted to these sorts of foodstuffs. Thsi also seems to fly in the face of the notion that it takes hundreds of thouisands of years to adapt to changes in our environment.

I'm not questioning the idea that low carb is the way we are adapted to eat. That seems obvious based on what it does for your body. But I'm wondering if we aren't capable of adapting to grains faster than people want us to believe. Certainly not within any one person's lifetime of course.

Anybody other amateur evolutionary biologists have opinions on this subject? It would seem to be an area of the philosophy behind low carb, that is open to criticism.

I absolutely agree with you. There are many studies within evolutionary biology that have observed periods of rapid genetic drift within populations, usually due to stochastic changes. The finches of the Galapagos are a well-known example in which dramatic selection was documented within a few decades.

It may also be true that some characters are more susceptible to change than others. I would guess that metabolic adaptations that involve so many different mechanisms may fall into this category, and it would account for the wide range of food tolerance that we see among different people. I visualize it as a standard bell-curve though, with healthy high-carbers (in America at least) currently falling way into one end of that curve.

My personal opinion is that unless we see more of a general dietary shift towards LC, the current epidemics of obesity and diabetes are going to function as a "selection event" that may result in a higher proportion of carb-tolerant folks over time. The rest of us poor maladapted folks are going to just die off before we have time to reproduce much. Fertility issues are often linked with insulin resistance too, especially in women.

Doesn't natural selection sort of assume that you get killed off before you breed? I think the problem of adapting to carbs is that it tends to make problems after your reproductive years, for the most part. Some carb problems, like PCOS, keep women from being fertile, so perhaps that will get bred out eventually.

Then again, I don't really think carbs are the whole story. I think its carbs in combination with lack of physical activity. And I don't mean a trip to the gym everyday, I mean.... physical labor each day. Cars, desk jobs and the whole lot keep us from using up the glucose.

That part of the equation is new, really only in the last 50 years or so we've gotten to this level of indolence.

That is true about selection being most effective pre-repro, but then again obesity in our kids is rampant as well, so I suppose the selection against carb-intolerance is exerting its effects.

I was just telling our secretary, who just got an exercise bike, that she needs to hook it to a generator to get some use out of all those calories. And I count mowing the lawn as an aerobic workout, although I still put it off and went jogging last night.

Never thought about it, but diabetes and obesity ARE natural selection at work. Good point.

not sure we'll ever 'adapt' to carbs in that they won't affect an insulin reaction, I think that's just how we're made

in the distant past, people often didn't live long enough to become fat in middle age--which was old age back then

also the activity level was far different than today, once agriculture was developed, people got fat if they were of the leisured class. I remember reading somewhere that if the women in a sheik's harem were fat, that was a status symbol as it showed the world he had an abundance of food. So people did put on weight even back then.

as far as some races being more lactose tolerant than others, I think that is also 'how they're made,' not an adaptation

the reason for and function of the different races is not really known very clearly, if at all. It's my very unscientific opinion, based on observation, that some of us have lower cholesterol and some are lactose intolerant, and it's just a part of our genetic make-up.

have no way of proving my hypothesis though!

Not at all. A better way of looking at it is "fitness": how many offspring will you produce and also how well will those offspring survive and reproduce. This is evolutionary "fitness", not exercise "fitness". Physical attractiveness, mood stability, etc. can be considered factors as well as health and fertility. (This is where evolutionary biologists start talking about sexual selection as well as natural selection as being important in changes within populations over time.) And your fitness is all completely relative to anyone else's fitness.


Probably not, if those genes really did start to become less frequent in the population they would be eliminated much more slowly and eventually just get stuck. Many recessive defects become "sheltered" in the heterozygote individual, once they reach a particular low frequency they just circulate around in the gene pool at that rate, unless of course some event occurs that increases their frequency again. The genetics of the Pima Indians are an example of that, where for centuries environmental conditions actually selected for the genes that now cause insulin resistance.

Here is how I understand it...

Of our genetic material there are genotype traits (your species) and phenotype traits (variance among members of a species).

The genotype is everything that all members of a species have in common. Because you can assume how difficult and time consuming it must be to spread a trait and cement it so deeply, an evolution in genotype and the evolution of species takes thousands and thousands of years of selection.

Phenotype is everything "else" in our genes, the subtle variances that makes us individuals. Changes in phenotype tend to be relatively insignificant, they may give an advantage or disadvantage relative to other members of your species (i.e. those with the same genotype) in varying environments, but generally speaking phenotype differences are small. The more related you are to another member of your species, the more insignificant the difference in phenotype will exist. For example, members of a nuclear family are very very similar and have relatively small differences in phenotype. They are so closely related they often can be mistaken for twins (like me and my sister often are). Then there are collections of families within a race. Families of humans which come from similar environments have more significant differences than related individuals, but they are still relatively small. Finally there is race. The difference between collections of families from different environments have an even more significant difference, but still in the grand scheme of things even racial differences are relatively insignificant. They are still confined to things like skin, eyes, hair, and other slight and/or superficial variances.

In other words, all ways in which humans are different among themselves is a phenotype difference. Changes in phenotype come about in response to recent (well recent on the evolutionary timeline) and/or subtle changes in environment. Blacks have dark skin because of the strong african sun. Higher melanin concentration works like built in sunscreen to protect them from it. On the other hand, whites have light skin because the frigid north did not give them enough sunlight, so they adapted by selecting for a paler complexion more sensitive to sun. The significant lack of melanin in the european complexion was an advantage... it allowed him to make the most of the sunlight he did get. The recessive nature of a light complexion implies that it is a more recent change, which implies that the phenotype of europeans (and all associated traits) are relatively new.

So you see human groups selected for different complexions due to the different environmental pressures in the regions where they lived, but these changes are so small and transient that they are not characteristic of an evolutionary branch off into two separate species. Despite superficial differences, blacks and whites share the same genome and are most definitely the same species.

Metabolic preference among races/families/individuals is also reflected by phenotype. Africans, native americans, australian aborigines and other newly modernized hunter gatherer peoples do very poorly with the grain based diet that european man eats. They never were exposed to it before, so they have a very low tolerance for these insulin spiking foods. Unsurprisingly their rates of obesity, diabetes, and heart disease are much much higher than white man. The insulin-sensitive phenotype is much more prevalent in the white racial group as it was an evolutionary advantage, since white people switched over to a very grain based diet.

Even though grain dependent cultures did start to partially adapt to the diet, we've been introduced to grain so recently that we, the human species, mostly still can't do well on it. Some phenotypes (those that descended from grain dependent cultures in particular) are very insulin sensitive and have a very low susceptibility to obesity, diabetes, and heart disease. For most of humanity this is not true.

The difference between genotype and phenotype is kind of like other classifications systems invented by man - it tries to make exact something which in nature is not exact and is far to expansive to ever be classified and organized. There is no hard line objective difference at which point a change is so prevalent and so intrinsic and so crucial that you have "old species" and then "new species". Humans invented the definition of a "species" and "genotype" and "phenotype". It is an entirely subjective classification. In nature there is no such thing as a "carnivore" and an "omnivore" and a "herbivore". There are no hard lines. For example, almost all carnivores eat some vegetation. Many herbivores eat insects and will eat meat if they can. Many if not most omnivores are not as unbiased as the label would imply, for example human beings have a distinct metabolic preference for a primarily meat based diet.

This is just of course my largely uneducated opinion on the subject so take this with a hearty grain of salt ;).

Ah no, genotype is our personal collection of alleles, our own DNA, and phenotype is only the physical expression of this. There is quite a lot of genotypic variance among different populations of humans, although of course less then between a human and say a chimp or a turtle, its all relative. Some genes are dominant - you only need one allele to have "it", some can express "partial dominance" - like the intermediate mocha skin color of the child of an interracial couple, but many recessive alleles simply don't express at all if the individual is heterozygote - but it is there nevertheless in your genotype, but not your phenotype. Heritability is phenotypic variance measured through genotypic and environmental factors - so yes, families members tend to resemble one another because they share more traits in both ways.

As was said, some humans (the ones who have been exposed to it longer) have already begun adapting to agriculture, at least better than their unexposed counterparts. So I guess my point in this is, that the idea that we as a species are going to take hundreds of thousands of years to adapt to grains, is out of line. On the other hand, it is clear that we are not there yet.

Which brings up another question. Are we lc-ers messing up our heirs by not exposing ourselves to the products of agriculture? Are our great grandkids going to be less tolerant of grain as a result of us foregoing it now?

Ah I see, thanks for clearing that up. I assumed that the genotype and phenotype distinctions was basically a way of identifying variance within species which aren't significant enough to classify as different species all together. So basically genotype is all the information you can pass on, and phenotype is the expressed result.

Thanks for clearing that up :). Like I said I am really uninformed on this topic, was just my uneducated opinion... I'm over my head here so I think I'll just read what those who are informed have to say :D

If we had to be informed to say something around here, I'd have to remain silent most of the time. And you know that would just kill me.

I did take genetics courses, and worked on corn genetics and photosynthesis in grad school. Fortunately, I didn't improve corn any. Still, I'm so ashamed.

I think the problem with carbs comes later than agriculture. Agriculture has been around a whole lot longer than heart disease and type 2 diabetes. Atkins said heart disease was virtually unknown before 1900. I think that's not quite right, probably super wealthy people who didn't do much got it.

But people worked much, much harder. Even the middle-class. People had to iron clothes, sweep the floor, hand wash stuff, kneed bread by hand, even as late as the 1970's and 1980's!

Before electricity... wow! Life was a lot harder. You might have to go to the water pump for running water, go to the outhouse to relieve yourself. No refrigeration for the most part. Wood burning stoves. All that activity uses up the glucose from your starchy meal.

My mom is 85 years old and I hear stories of what life was like back then. Obesity was rare. Some people, like my Mom, were plump, but just because you were a little fatter than normal, didn't mean you were unhealthy. Just like it doesn't today. Your underlying physical fitness is the indicator of whether or not your healthy. And most of the people back then were pretty physically fit. At least the ones leaving rural lives, like my parents did.

Not everyone keeled over in middle-age. In fact, lots of people lived into their 70's and 80's and beyond. Benjamin Franklin was a very vigorous man until just about the end of his life. He lived to be 85 years old. People died from epidemics, infections, accidents, diseases spread by sanitation issues and bugs and child birth a whole lot more. But I don't think they died from Type 2 diabetes and heart disease anything like they do now.

Just my uninformed opinion:

I think this is because we are in a second stage of natural selection by over carbing. The first stage was during the beginning of agriculture when grains were first consumed on a regular basis. People particularly unsuited to carbs would have gotten sick pretty quickly (like the native americans and african bushmen did) upon exposure to these new foods. Of course, the people had no idea why some of them were sick and dying of mysterious illness. Of course, only the ones who were susceptible enough to sicken before reprodution would have prevented the genes from being passed on, though.

The second stage began around 1900 when a more highly refined white flour and sugary drinks started being used massively. That is the difference between paleo and Atkins. Paleo dieters recognise the first stage and Atkins only sees the second. For everyone, though, I think a return to carbs as close to the ones the paleolithic hunters ate is better than simply returning to 1900.

It is important to note that the genes susceptible to this second wave of "white death :) " will probably NEVER be removed by natural selection. Why? Because we now have the medicince to keep alive a 10 year old type II diabetic. He or she will now grow up to reproduce. When the first white death happened, these would have died before reproduction.

:lol: If I recall correctly, breeding corn is often working with additive variances. I notice that you are knowledgable about metabolic processes, so I guess the relevant questions here are what metabolic characters are vulnerable to selection and at what point do you begin to see gross changes?



I think if we look at the overall history of human evolution (and just when did that precisely begin?) we'll see this same story repeated over and over. The Pima Indians probably aren't susceptible to carbs the way they are by chance alone - their lifestyle and diet selected for those characteristics. In other words, their tendency to IR and obesity today is what helped them to survive and thrive in the conditions of yesteryear. And I do agree with Nancy that the intense physical demands on generations of our ancestors, which suddenly no longer exist for many of us, play a large role in the health problems we develop nowadays.


This is ice cold evolutionary biology here, not the spiritual stuff about how we are all wonderful inside. I believe we are biologically hardwired to respond to people who appear healthy, have good waist-hip ratios (in women, a sign of reproductive health), symmetry, cranio-facial neoteny (fascinating stuff), and we do not respond as well to people who appear unhealthy in some way, or have signs of developmental abnormality. Dawkin's "The Selfish Gene" comes to mind as a good book that deals with this stuff. So that's why I predict reduced evolutionary fitness for people who become unhealthy from diet (or whatever), even if they are perfectly capable of reproduction. There will be more of those folk who want to but don't then among people who radiate health, if you know what I mean. And if their kids inherit the same health problems they will face the same fitness challenges as their parents did. So, due to "heterozygote sheltering" those genes will always be with us, but their proportions will simply change within the population.